Car retarder control system

ABSTRACT

A control system for a railway car retarder to be used in a classification yard. The control system includes a digital computer which is programmed to compute a braking pattern for each car or cut of cars which is to pass through the retarder. Taking into account the characteristics of the cut and its velocity in entering the retarder, the computer determines a braking pattern which will slow the cut of cars down to the desired exit velocity so that the cut will traverse the remaining portion of the classification yard and couple to the preceding cars without excessive speed. The braking pattern is that which will decrease the velocity of the cut from its entering velocity to the desired exit velocity using the maximum amount of retarder length as is possible. In this manner, the braking force the cut is subjected to is minimized consistent with decreasing its velocity by the desired amount.

States Patent 1 DiPaola et al.

[ CAR RETARDER CONTROL SYSTEM [75] Inventors: John J. DiPaola, Penfield', Charles W. Morse, Rochester; Richard A. Dobson, Caledonia, all of NY.

[73] Assignee: General Signal Corporation,

Rochester, NY.

Primary Examiner-M. Henson Wood, Jr. Assistant ExaminerGeorge H. Libman Attorney, Agent, or FirmMilton E. Kleinman; George Vande Sande; Harold S. Wynn [451 Oct. 29, 1974 [5 7 ABSTRACT A control system for a railway car retarder to be used in a classification yard. The control system includes a digital computer which is programmed to compute a braking pattern for each car or cut of cars which is to pass through the retarder. Taking into account the characteristics of the cut and its velocity in entering the retarder, the computer determines a braking pattern which will slow the cut of cars down to the desired exit velocity so that the cut will traverse the remaining portion of the classification yard and couple to the preceding cars without excessive speed. The braking pattern is that which will decrease the velocity of the cut from its entering velocity to the desired exit velocity using the maximum amount of retarder length as is possible. In this manner, the braking force the cut is subjected to is minimized consistent with decreasing its velocity by the desired amount.

12 Claims, 8 Drawing Figures Cor ChOI'GCiGrISiICS PMENIEH 0H 2 9 mm FIG. 20.

Compure Y 24 25 1 Compute S1 Determine M n. Tlme Store In Table Con mute 32 New SL Compute TransnlonTlme Update Vf 1/3 Update Pos Total Time And DISTGHCG SetAPTo MIMI! Set X To ,/38

Newvalue Re IaceS P reviou'sgy 40 Remove Nexi FIG. 2E.

58 Add All TotalDist.

Calc.

. 59 Determine Remaining are 1; DisHn Open V dd j A ToTo'ra Dist In Open CompuTeTime In Open 63 SToreAsTime lnOpen 64 Add ToToTal TlmelnOpen Return mmcnnmze m4 3.844514 SHEU u of 4 FIG. 3.

Compute E ntrunce Speed I05 so Se? s ,e9 I03 Set A Rom 'Cor v Choroctenstlcs Gate Set Next A 75 ComputeTlme Distln Pos.

Sfo re 75 C0mpufe, ven IOG/ CPU Table COmD '08 7| IO? '0' 32) Q CAR RETARDER CONTROL SYSTEM BACKGROUND OF THE INVENTION In a classification yard, a train of railway freight cars is pushed over the crest of a hump, and each car is then allowed to roll by gravity down the hump and over a number of route-selecting switches to a particular one of a number of destination tracks. When several successive cars are to go to the same destination track, they are usually left coupled together and allowed to roll together to their destination track; such a group of cars is called a cut. In this way, the cars of a train are classified according to their intended destination. Hereinafter a cut will be referred to even though it may consist of only one car.

The grade of a hump is made sufficient so that the car with the hardest rolling characteristics can reach the most remote destination in the classification yard and couple onto other cars in that same destination track. Easier rolling cars must, consequently, be decelerated so that they too will reach their destination tracks at a suitable coupling speed. This deceleration is accomplished'by providing car retarders along the track rails whose brake shoe beams apply a controllable braking force to the rims of the car wheels.

The earliest car retarders used in classification yards were manually controlled by an operator who visually observed the cut proceeding through the retarder, and. with knowledge of the cat's destination track, selected an appropriate braking force to be applied to the cut. Difficulties with properly estimating the amount of deceleration required has led to the use of automatic car retarder. control apparatus. In the past, a variety of schemes have been used, some of which employed radar speed measuring apparatus to measure the speed of the cut through the retarder and computing apparatus to compute the desired cut velocity through the retarder. The apparatus would compare the desired cut velocity with the actual cut velocity as determined by the radar speed sensing apparatus and approximately control the retarder. The complexity of this apparatus and difficulties found in its use have led to the desire for a digital approach to the control of a car retarder along with the elimination of the radar speed measuring apparatus in the control loop.

In some prior art systems for control of car retarders, the retarder has been preset, prior to the entry of a cut into the retarder, to provide a predetermined braking force dependent primarily upon car weight, with a greater degree of braking force being applied to cars which are classified as being heavy. In addition, computations have been made for each cut taking into account a plurality of different parameters with the objective of determining an appropriate relase speed from the retarder. Thereafter, as the cut progresses through the retarder, its speed is continually monitored, and the retarder is released when the speed of the cut has been reduced to a value at or near the precomputed release speed. Some systems of this general type have further provided for a reduction in the braking force of the retarder as the cut proceeds through the retarder. One disadvantage of such prior art systems has been that the retarder was released at a time prior to the cuts reaching the exit end of the retarder with the result that the speed of the cut at the exit end could by that time have reached a value different from the precomputed, de-

sired retarder release speed, thereby introducing error into the system. Also, such a prior art system has re sulted in the application of a higher degree of braking effort, particularly at the retarder entrance end, than is actually necessary to reduce cut speed to its desired release speed at the retarder exit end, thereby resulting in unnecessary wear on the retarder brake shoes and at times also tending to force the wheels of a car out of the retarder.

Furthermore, some of the prior art systems which employ feedback in the control loop subject the retarder to a large number of different orders during the passage of a cut. This reduces the life of the retarder mechanism. In particular calling for a low braking effort and then a higher braking effort subject the retarder to extreme wear and this type of operation should be avoided The system disclosed in this application employs a digital computer to compute a retarder braking control profile for each out which is to traverse the retarder. The profile is computed so that the maximum amount of retarder length can be utilized which minimizes the amount of braking force applied to the cut at any instant of time. The cut characteristics, the retarder entering velocity, and the desired exit velocity are used in the generation of the retarder braking control profile. The actual retarder control profile is a series of commands for the retarder, directing it to one of a plurality of positions to exert one of a plurality of corresponding braking forces on the cut in the retarder. Since the present invention is not concerned with aspects of the overall retarder control problem such as determining I the rollability characteristics of the cut, the weight of the cut, its entering velocity and computation of exit velocity, the details of apparatus to perform these functions will not be disclosed herein. Apparatus to perform these functions are disclosed for instance in US. Pats. Nos. 3,054,983, 3,110,461, 3,217,159, 3,253,141, and 3,268,725, all assigned to the assignee of the present application.

SUMMARY OF THE INVENTION The present invention provides a control system for a car retarder used in a classification yard which maximizes the distance over which the retarder is used. It is a corresponding object of the present invention to minimize the amount of braking force applied to the cut in the retarder at any particular instant of time consistent with the necessity to reduce the velocity of the cut to the desired exit velocity.

It is another object of the present invention to utilize a properly programmed digital computer to compute a set of braking commands for a railway car retarder in a classification yard so that the retarder will be utilized for the maximum length and which minimizes the braking force as is consistent with the necessity to decrease the cut velocity to a desired exit velocity. It is still a fur ther object of the present invention to provide a system which meets the foregoing objectives and at the same time eliminates the necessity for controlling the retarder in accordance with the actual cut velocity as the cut proceeds through the retarder.

Furthermore, it is an object of the present invention to compute a braking pattern for a retarder in which the braking effort, if caused to change, will decrease as the cut proceeds through the retarder.

It is a further object of the present invention to eliminate the necessity for continually sensing cut velocity in the retarder and thus eliminate the necessity for radar speed measuring devices in the control loop.

BRIEF DESCRIPTION OF THE DRAWINGS In describing the invention in detail, reference is made to the accompanying drawings in which:

FIG. 1 is an explanatory graph of velocity versus distance of a theoretical cut in a retarder;

FIG. 2A is a flow diagram of a portion of the program utilized in the instant invention entitled enter RC PG;

FIG. 2B is a flow diagram ofa portion of the program used in the present invention entitled start";

FIG. 2C is a flow diagram of a portion ofthe program used in the present invention entitled next;

FIG. 2D is a flow diagram of a portion of the program used in the present invention entitled over";

FIG. 2E is a flow diagram of a portion of the program used in the present invention entitled done;

FIG. 3 is a flow diagram of a portion of a program utilized in the present invention entitled V and FIG. 4 is a schematic showing the inter-relationship of apparatus used in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 4 shows the schematic form of the apparatus utilized in accordance with the present invention to effect proper retarder control. The portion of the trackway 100 shown in FIG. 4 represents a portion of the main trackway in a classification yard and, in accordance with normal practice, the physical track would exist on a downgrade of known slope. The retarder 104 is preceded by a number of wheel detectors 105. Each of the wheel detectors provides an input to the central processing unit 101. The central processing unit per se is a digital computer of known form which is provided with the information necessary to compute, in accordance with the program disclosed in FIGS. 2 and 3, the retarder braking control profile. The wheel detectors, sensing the time of passage of the first axle of the cut, enable the central processing unit 101 to determine the velocity of the cut.

The retarder 104 is controlled by the retarder operating mechanism 103 to apply a controllable braking force to the cut as it proceeds through the retarder in order to decrease the velocity of the cut to the desired exit velocity. Since it is the force exerted by the retarder on the wheels of the cut which is controllable, one of the factors which must be taken into consideration by the central processing unit 101 is the mass of the cut. From the well-known formula that acceleration is equal to force divided by mass, the central processing unit 101 can determine, for any given mass and any given force, the acceleration that the force will exert on the mass.

In addition to the car velocity information received by central processing unit 101 from the wheel sensors 105, the central processing unit 101 also receives further information related to the cut characteristics for which the retarder control profile is to be generated and receives these characteristics over line 106. The central processing unit 101 requires information as to the length of the cut, the length of the first car of the cut if there is more than one car in the cut, and the total mass of the cut. Furthermore, the central processing unit 101 receives via line 107 a precomputed exit velocity for the cut. The program discussed with respect to FIGS. 2 and 3 is designed to control the retarder so as to reduce the cuts initial velocity to this precomputed exit velocity. In addition, permanent information stored in the central processing unit 101 is indicative of the characteristics of the retarder. For instance, the various levels of braking force available by the retarder are available. Furthermore, for each of the different braking positions of the retarder there is a minimum allowable time in that position and also a transition time, i.e., the time it takes for the retarder to move from one braking position to another.

With the aforementioned information and the programs discussed with respect to FIGS. 2 and 3, the central processing unit 101 can generate a retarder braking control profile for a particular cut. The profile consists of one or a series of discrete braking position commands along with the time duration during which that command is effective and the computed distance the cut will travel with the retarder in that position. The profile is stored in table 102 so that the profile information can operate retarder operating mechanism 103.

Table 102 is a schematic showing of a portion of a memory device to store retarder operating controls and, physically, may be a part of the central processing unit 101.

The clock, 109, is started when the car enters the retarder and comparator 108 determines, based on the times stored in the tables 102, when a particular braking command is to be effective. At such time the comparator 108 causes the command to be transmitted to ROM 103 by gate 110.

Since tables 102 store, in addition to the time span for each braking command, the distance traveled by the cut during that command, the control could also be on a distance basis. That is a track circuit and A/D converter could be substituted for clock 109. The comparator 108 would then perform a distance rather than time comparison but the control would proceed in the same manner as discussed above.

Prior to describing, in detail, an embodiment of the present invention, it will be helpful to describe first a simplified embodiment to illustrate some of the basic principles of this invention. FIG. 1 is a graphical representation of theoretical cut velocity versus distance through the retarder.

As this description proceeds it will be apparent that some relationship must be assumed for the variation in cut velocity with distance through the retarder. The linear relationship shown in FIG. 1 has been chosen as practical and easy to mechanize.

Furthermore it meets one of the objectives of the invention, i.e., to use as much of the retarder as possible within the practical limits of the problem. It should be stressed that the linear relationship is used only as a starting point for the computations and the variation of actual cut velocity with distance through the retarder is shown by the non-linear portions of FIG. 1.

To obtain a linear cut velocity representations as shown would require constantly varying the braking force exerted by the retarder on the cut. The expression V ,lVF-l-2AX expresses the relationship between the initial velocity (V,-) and exit velocity (V,.) under constant deceleration (A) over the braking distance variable X. Since this is not a linear function, any constant deceleration will not produce the straight line relationship between car ve locity and distance as expressed in FIG. 1.

The present invention attempts to maximize the distance over which the retarder is effective by determining the degree of retardation which must be applied to the cut as it travels through the retarder to obtain the desired objective, i.e., a cut velocity at the exit end equaling the precomputed exit velocity. Since the apparatus of this invention is particularly adapted for use with retarders which are operable to provide a plurality of discrete levels of retardation, the apparatus first computes the distance necessary to reduce the car's initial velocity to the desired exit velocity on the assumption that only the minimum braking force is to be used throughout its travel through the retarder. If this distance is greater than the effective retarder length, it is apparent that the minimum braking force will not be sufficient if applied over its entire length. However, to maximize the retarder length which is utilized, the present invention then proceeds down the theoretical profile, i.e., the straight line 6, and attempts to fit minimum braking to the remainder of the constraints. A brief example will suffice. The numerical values used here are chosen for illustrative purposes only. Clearly some of the values chosen would not be met in practice. Assume, asshown in FIG. 1, that V,=60 feet per second and V,.=l0 feet per second, and that light braking cor responds to a deceleration of feet per second per second. The first computation employing the formula D=(V,- V,. )/2a shows-a required length over 87 feet.

Since this is greater than the 50 feet we have assumedfor the retarder length, we will move down the theoretical velocity-versus-distance profile at equal distance increments (i.e., such as one foot increments) and repeat the computation. When we reach point 4, at 30 feet per second, some 30 feet through the retarder, the computation will be performed with v,=30 feet per second, V,.=l0 feet per second and will indicate that an effective retarder length of 20 feet is required. Since this is exactly (the equality between remaining length and required length is not required, it is only necessary that the required length be less than or equal to the remaining length) the amount of retarder left at this point, the computation has shown that it is permissible to use light braking, corresponding to a deceleration of 20 feet per second per second, if we can achieve a car velocity, at a point 30 feet through the retarder, of 30 feet per second. Thus, a portion of the problem has been tentatively solved.

A prerequisite for the foregoing solution was the deceleration of the car from 60 feet per second initial velocity to 30 feet per second intermediate velocity through 30 feet of the retarder. To determine if this is possible, we can use the above formula once again,

final velocity of feet per second and a deceleration of 40 feet per second per second. This will show that 20 feet of retarder length is required. This is exactly (as above, the equality between remaining retarder length and required retarder length is not necessary) what is available and therefore a second portion of the problem has been tentatively completed.

The only remaining portion is to determine if a still ln summary, the braking of our assumed car would begin at a deceleration of 60 feet per second per second and would continue until the car has traversed 7% feet of retarder at which time its velocity would have decreased to some feet per second. At this point, the retarder is controlled to apply a deceleration corresponding to 40 feet per second per second which would continue until the car has traversed an additional 20 feet through the retarder at which point its velocity would now be down to 30 feet per second. At this point, the retarder control would again be changed to apply an effective deceleration of 20 feet per second per second for the remaining 20 feet of the retarder length. The car would then exit from the retarder with a velocity of 10 feet per second. Thus, the retarder is to be utilized over 47% of its total of 50 feet and the car has been slowed with the maximum amount of light braking that is possible. Furthermore the braking effort, when changed, has always decreased.

The above example is only illustrative, as it obviously uses speeds, distances, and deceleration factors which might not at all be met in practice. Furthermore, the above example ignores the transition effects in changing the retarder effective deceleration and also ignores the acceleration of the car in the retarder when it is in the open position. The above example does however illustrate the manner in which the-computation proceeds from the exit end of the retarder toward the entrance end and attempts to fit the car and retarder characteristics to an optimal velocity-distance profile.

FIG. 2A shows the first portion of the routine entitled RCPG, standing for Retarder Control Profile Generator. As has been previously explained, this program, taking into consideration the desired exit velocity of the cut, and the braking effect of the various retarder braking positions available on the cut, and the cuts entering velocity, will generate a series of orders for the retarder control. These orders will determine when, and to what, positions the retarder is directed to during the time that the cut is subject to action by the retarder.

The first step 10 in the program is to clear the tables. The orders which the program generates for the retarder control are stored in the table and clearing the table ensures that it will accumulate only orders with respect to the cut which is presently under consideration. The next step, 11, sets the current acceleration equal to light. The term acceleration is used in the generic sense, that is, covering both acceleration and deceleration. The braking force that the retarder exerts on the car or cut is thus properly termed an acceleration although in the algebraic sense it is a deceleration.

Furthermore, the retarders which this program is designed to control have a number of discrete positions available. such as open, light, medium. heavy, and extra heavy. Of course, in the open position, the retarder would have no braking effect on the cut, in the light position some braking occurs, and in the medium, heavy, and extra heavy positions more and more braking is effected. The step presently under discussion, ll, merely sets the initial trial retarder position to light. This is in keeping with the general purpose of the program which is to control the retarder to utilize as much retarder length as possible. In line with this goal, the program attempts to fit the fixed parameters; entering velocity and exiting velocity, to a retarder control profile which utilizes the minimum possible braking effort at any one time.

The next program function, 12, is to set a parameter for previous acceleration (AP) to open. The computations performed by the program utilize, in addition to various velocities, parameters for current acceleration and previous acceleration. This function, 12, sets the previous acceleration to the open position.

At this point it may be helpful to the reader to say a little about the term previous, as previous acceleration or previous starting velocity (which will come up shortly). The discussion with respect to FIG. 1 showed how the retarder control profile is computed separately for the different braking efforts required. After the tentative solution for light braking (between 30' and 50' on FIG. I) was arrived at an intermediate braking computation was made (between 10' and 30' on FIG. 1). In this manner the braking control profile is built up from the exit end of the retarder. It is in this sense that the word previous is used. Therefore the light braking (between 30 and 50' in FIG. 1) is previous" to the intermediate braking (between 10' and 30' on FIG. 1) because it is used first in the computation. In the same sense for the exit transition computation from light to open the previous acceleration (AP) is open and the present acceleration (A) is light.

The function clear repass work", 13, is an internal record keeping function. Depending upon the results of the various trial computations that are made the repass word may be set to keep track of the completeness of the computation. For instance, it may become necessary to know whether or not a previously computed partial solution has been rejected for one reason or another. The condition of the repass word is then significant. However, prior to when it becomes necessary to set the repass word, this word should be cleared. This function, 13, ensures that the repass work is cleared.

The next function set final velocity" (V 14, sets a parameter used in the computation (V,) to be equal to the exit velocity. The exit velocity is obtained in a manner well known in the art, based upon the classification track to which the cut is directed, its distance from the retarder, the profile of the terrain to that track and the weight and rolling characteristics of the cut. A typical example showing apparatus to perform an exit velocity computation is shown in prior US. Pat. No. 3,217,159.

Subsequently, the exit velocity is also stored as the previous starting velocity in function 15. This is an other program parameter that will be utilized as the computations proceed. Finally, at function 16 the parameter distance left" (SL) is set to be equal to the total retarder length plus the total wheel base of the cut minus the first wheel base of the cut. It is normal classification yard practice to handle all directly adjacent cars which are destined for the identical classification track as a unit or cut of cars. Of course, if there are no such directly adjacent cars destined for the same classification track, a cut may be made up of only one car. In those cases the distance left (SL) would be merely the retarder length since the other functions of adding in the total wheel base and then subtracting the first wheel base would cancel out. However, where a cut is made up ofa number of cars, the distance left (SL) will be equal to the total retarder length plus the total wheel base of the cut less the wheel base of the first car in the cut. This is the effective length of the retarder for that cut. Since all cars in a out are coupled, if any one of them is in the retarder, the retarder is effective on the entire out. That is the basis for computing the distance left (SL) in the manner just stated.

From function 16 the program proceeds to the routine start.

Start is shown in FIG. 28. Start performs some basic computations related to a transition and also initializes the program so the computations contained in OVER can be performed. The explanation of FIG. 1, the simplified description, stated that the transitions in braking had been ignored. However, to refine the accuracy of the computation, the transition periods in the actual program are not ignored. When a retarder changes position, that is, when it changes from one braking effort to another, the braking force and the resulting acceleration imparted to the cut will be somewhere between the value imparted by the previous position and the value imparted by the new position. Since the program computations proceed from the exit end of the retarder and build up the control from that end, this first transition to be computed concerns the last transition of the retarder operation, i.e., from some braking position to the open position.

The first function, 17, computes average acceleration (A during the transition from light braking, which had been set at function 11 and the open position, which had been set at 12. The computation proceeds accordng to the formula: A =(A+AP)+2.

To compute further the parameters in this transition, it is necessary to know the time delay during which the transition takes place, that is how long does the retarder take to traverse from the light to open position. This is a precomputed time which merely requires reference to a table and is accomplished in function 18.

Although the exit velocity of the cut is a precomputed parameter, it is now necessary to determine the theoretical cut velocity when the retarder initiates the transition from light braking to open. This computation is performed at function 19 according to the formula V=Vfl'(A+AP/2) T where V had been set previously as the exit velocity, the expression (A+AP)/2 is the average acceleration during the transition and T,, is the time taken by the transition. This computed velocity is the velocity the cut should have when the retarder begins its transition from light braking to open.

It is now also necessary to compute the retarder length covered by the cut during the transition period and this is computed in function 20 where SL, is equal to the distance taken during the transition period and is found by computing the function (V V, )/2A, Since this retarder length must be available for the transition to take place, it is retarder length which cannot be utilized in any particular braking condition and therefore must be subtracted from the available retarder length computed in function 16. Therefore, function 21 updates a new retarder distance left (SL) by subtracting from the previous value the justcomputed SL Functions 22 and 23 initialize the program for the computations to be performed in OVER. In the simplified description, and accompanying drawing, FIG. 1, it was explained that a linear relationship between car velocity and distance through the retarder could not be obtained with a single value of acceleration; nevertheless, this is the assumed profile which is a starting point for the computations. It should be understood that other profiles could be assumed and used in this program. A particular constraint on the selection of an assumed profile is the time necessary to compute the parameters of the profile. The time available for these computations is limited by the time the cut takes to travel from the wheel detectors to the retarder. It is now necessary to have available the characteristics of this assumed profile. They are the velocity intercept, V,.,,', which is computed by the program V,,,,, to be discussed later, V the exit velocity, the computation of which has been discussed above, and the slope of the line whichis simply V minus V divided by S where S equals the maximum retarder length. Upon completing the computation of these parameters, the program proceeds to OVER which is shown in FIG. 2D.

The first function in OVER is to compute a trial point on the slope of the line, which is accomplished by function 24. The computation is performed using the equation Y=(AL) X+BL where AL is the slope previously determined and BL is equal to V and X represents distance through the retarder. On the first pass through this routine, X has been set to zero by function 22. The computation then will result in y=V,.,, since V equals BL.

The next function is to compute a distance S which is that required at the assumed braking to decrease the cars velocity from Y to V, and this is performed in function 25. The computation of S is determined by the equation (Y V) /2A.

The next function, 26, is to compute the estimated distance left from the formula SLX and since on this first pass, X equals 0, then the estimated distance left would merely be SL. Decision point 27 determines if S is less then SLX and, assuming for purposes of discussion, it is not, then the program proceeds to the decision point 37 which determines whether or not this is a repass. In accordance with our example, this is not a repass and therefore function 38 would set X to a new value, higher than zero. Subsequently, decision point 39 determines if X is equal to SL and, further assuming that it is not, proceeds to repeat OVER. What has been accomplished in this loop is a determination of whether or not light braking will suffice from the initial velocity, V,,,' to reduce the car velocity to the required velocity V in a distance which is equal to or less than the available distance, SL. Since we have postulated, by the result of decision point 27 that S is not smaller than SL, then we have incremented X. What we are doing is proceeding along the line shown in FIG. 1, the assumed profile, and attempting to find an intermediate point in the retarder from which light braking will be sufficient to achieve the desired velocity V. On the next pass through, OVER function 24 will compute Y with the new value of X and this will be somewhat less than the previous value of V,,,,'. As before, a new distance is computed and the estimated distance left SLX is again computed and this value is compared to the necessary distance.

The incremental value by which X is changed during the performance of each loop depends upon a number of considerations. Clearly, the smaller the incremental value, the more accurate the computation will be, and also the computation will take a longer amount of time to proceed down the line from V to V Since only a predetermined amount of time is available for this routine to be accomplished, the increments added to X must be balanced between these considerations. In one embodiment of the present invention, the increment of X used has been one foot. This computation then proceeds in accordance with the simplified description to determine whether or not the assumed light braking will be sufficient from some intermediate point of the retarder to achieve the desired velocity V. Assuming that it is, then at some point in this looping process between functions 24 and 39, decision point 27 will determine that S is less than SLX and proceed to perform the computation to determine T (POS) by function 28. The formula used for this computation is (YV)/A. Function 29 determines the minimum allowable time in the assumed braking position. This again merely requires reference to a predetermined table. Decision point 30 determines whether this time is sufficient, i.e., whether or not it is longer than the minimum allowable time. If it is, then that time in position is stored in the table and a new distance left is determined by subtracting S from SL in function 32.

Function 33 computes the actual transition time as (V"' f)/A p- Function 34 stores the Y value at which S was first less than SLX as a new V; and then function 35 adds the transition time to the previously computed time in this position and distance in this position. Decision point 65 determines if this is a repass. If not, function 66 increases AP to the next level. Otherwise function 66 is omitted. Decision point 36 determines wheither or not the new V; is within the tolerance of V,.,,', the modified entering velocity. There is no assurance that any particular V will be identical to V and therefore if V, is within reasonable tolerance of V.,,, the computation is considered finished. If the computed V; is within the tolerance then the program proceeds to perform DONE whereas if it is not, then the program proceeds to perform NEXT.

It very well may be, however, that the computation proceeds down the slope of the line and never determines, at decision point 27, that S is less than SLX. Of course, each time this negative result is reached, decision point 37 checks to determine if this is a repass. Since we have assumed it is not, function 38 increments X to a new value. At some point, after a number of iterations of this routine decision point 39 will determine that X is equal to SL which will render function 40 operative to replace the transition distance previously removed at function 21. Thus, the new SL will be the old SL with SL, added back in. The same result is reached if at any time decision point 30 determines that the actual time in position, computed at function 28, is below the minimum time determined at function 29. In either event, the program has determined that the particulur brake setting is not going to be used and therefore the previous transition distance which had been subtracted at function 21 must be added back in and recomputed using a new value of current acceleration.

The program portion NEXT, shown in FIG. 2C, can be entered for one of two reasons. Either, during a trial computation for a particular brake setting, it is determined that that particular brake setting will not be used; then, after completing function 40 (FIG. 2D) NEXT is entered. On the other hand, if a particular brake setting computation is completed and decision point 36 (FIG. 2D) determines that V, is not within the tolerance of V,.,,, then NEXT will also be entered. In either case, decision point 41 determines whether or not this is a repass. Since, in the example under discussion, the repass flag has not been set, we will assume that it is not a repass and function 42 sets the acceleration level to the next value.

Decision point 43 determines whether or not this value of acceleration is allowable for the particular cut now within the retarder. Assuming that it is, the routine loops back to start and computes new transition values. If NEXT had been entered when function 40 determined that a particular brake setting would not be used, then it will be apparent that the current setting A is two levels above setting AP. Since the program, prior to function 40, had eliminated one of the braking levels, the transition now is between braking levels which are separated by an intermediate braking level. On the other hand, if the program portion NEXT had been entered subsequent to decision point 36, function 66, just prior thereto, would have increased AP another level so that when the transition computation, in START, is accomplished, the levels of A and AP would be adjacent.

The second and subsequent passes through START and OVER would perform computations very similar to those already explained, with increasingly higher braking levels. This would accomplish the functions explained with respect to the simplified description of FIG. I. That is, for the next higher braking level, the computation would begin with V,.,,' and determine if the distance left (SL) was sufficient to decrease the velocity of the car or cut to V;, as set by function 34. If it was not, then some further intermediate velocity along the theoretical velocity profile would be chosen, by incrementing X, and the computation would again proceed until the remaining distance (SL-X) had been reduced to zero unless a successful solution is found.

If no successful solution is found, or if the successful solution indicates a braking time which is below the minimum allowable, then this braking level will be deleted from the retarder control orders and NEXT would again be performed to increase the braking effort further.

In this fashion, the computation proceeds until V becomes equal to V,.,,', or within the tolerance range of V,,,' and the program is directed to DONE. On the other hand, if V, does not approach V, by the allowable tolerance, then at some point in the passes through NEXT, decision point 43 will determine that the acceleration is too great for the car or cut and function 44 will set V,,,, equal to Y, function 45 will set the repass flag, function 46 will set A back to one lower level (thus cancelling out the increment added in at function 42). Decision point 47 will determine whether or not this braking level corresponds to OPEN, and if not,

function 48 will set AP equal to A and function 49 will decrement AP one level.

The only reason the program would progress beyond decision point 43 in NEXT, is that the computations performed have indicated that with allowable braking forces, the velocity of the car has not yet been reduced from its V to the V in the allowable distance. Assuming that the AP set by function 49 is not open, as checked by decision point 50, then the program will look for a previous braking position which used a lower than maximum allowable braking force, and eliminate it and substitute the highest allowable braking force for the computation. If decision point 52 determines that the particular braking position was not used, the program loops back to function 49 to decrement the AP setting until decision point 52 determines that it has discovered a braking position that has been utilized. Functions 53 and 54 then revert to the previous distance left (SL) and previous time and distance totals existing prior to this braking. Function 55 clears the table of the stored values, thus eliminating all traces of this braking position and then directs the program to START to perform a new computation at a higher braking level.

Since this is a repass, the program portion OVER will only be performed once, and if decision point 27 determines the S is not smaller than SL-X, then the program will again be directed to function 49 to decrement AP to a still lower value and go through the same routine. In this fashion, previously computed lighter braking levels are deleted in turn to allow the highest braking effort to be exerted over longer and longer distances and attempts to find a solution which will reduce the entering velocity (V,.,,') to the required exit velocity (V,.,) in some allowable distance. Of course, if the problem is satisfactorily solved, the computed values are stored and the program is directed to DONE.

If, at some point in traversing NEXT, either decision point 47 or 50 determines that either the acceleration level is in effect open or the previous acceleration level under check is open, then the program is directed to set the distance in the current acceleration position to the maximum length of the retarder, at function 56, and the time in position is set to the maximum at function 57 and the program is concluded. In effect, decision point 43 has determined that the current acceleration is the highest allowable for the car and, either this is open or, all previous acceleration levels that had been selected for use have now been eliminated and therefore there is only one allowable acceleration force and this will be used to the maximum length of the retarder.

The program portion DONE is entered when the computations arrive at an entering velocity which is equal to V, or within an allowable tolerance thereof. This particular portion is shown in FIG. 2D, and the first function, 58, adds all the calculated distances that the car or cut will travel with the retarder in a particular braking position. Function 59 determines how much retarder length is left over and function 60 sets the retarder to the open position for this distance. Function which the retarder will remain open and adds it by function 64 to the previous total time the retarder had been set to open. That concludes the program.

The conclusion of the program leaves in a table, a series of times and distances for the different retarder braking positions. The retarder then can be controlled from this-table, either on a time or distance basis to change from one position to another. That is, on a time basis, a clock is started when the cut first enters the retarder and, after the time elapsed reaches the value set in the table for the retarder at that braking position, the retarder is controlled to the next braking level which has a time value in it and the clock is again atarted. In a like manner, the retarder is controlled to each of its positions for the predetermined period of time computed by the program for that position. It should be obvious that if distance sensing information is available, the retarder can alternatively be controlled on the basis of the computed table as the cut proceeds through the retarder.

In the program disclosed in FIG. 2, a velocity V, is utilized for computations. The program V,,,, shown in FIG. 3, is utilized to compute V,.,,'. The program V,., also computes the largest braking force that can be utilized as the car or cut enters the retarder in line with the other constraints placed upon the system.

The first function of V 67, is to compute the actual entrance velocity of the car or cut into the retarder. As shown in FIG. 4, a series of wheel detectors determine the time it takes for the first truck of the first car to traverse a known distance, and from well-known principles, the velocity can thus be determined.

The next function, 68, sets S, a distance, equal to the distance between the first and second truck of the car, or this distance with respect to the first car of a cut. Function 69 sets the acceleration to the highest possible braking force and function 70 computes a trial value for V,.,,. The expression relating V to V, (the initial velocity of the car entering the retarder) is V F =V,- 2AS. Decision point 71 determines that this trial value of V,.,,' is acceptable by determining whether it is greater than the exit velocity plus a factor for the cars deceleration through the retarder; that is, decision point 71 determines if V,.,,' V,.,+A (where A is the minimum velocity loss through the retarder). If it is, then this is an acceptable entry condition and the program skips to function 75 to compute the time and distance in this braking position which is then stored by function 76 in the tables for controlling the retarder and that will complete the program. Assuming, however, that the V,.,, is not large enough, that itis not greater. than V by a sufficient margin, then function 72 sets the braking force to a lower level and function 73 determines if there is such a lower level. If there is, then the program recomputes a new V,.,, using the new braking force and performs the same check by function 71. If this new V,,, is acceptable, then the program proceeds as discussed above. If it is not, then function 72 sets a new braking level and the program proceeds as discussed above. If it is not, then function 72 sets a new braking level and the program proceeds as discussed above. At some point, if an acceptable V is not found, decision point 73 determines that there are no further braking positions available and directs the program to function 74 where the retarder is set to OPEN.

In this fashion, the highest allowable braking level is used for the time it takes the first car to completely enter the retarder. The calculated values are stored in the table to control the retarder and the computed V,.,.', the velocity of the car when the second truck enters the retarder is made available to the program of FIG. 2 for its computations.

As is well known the braking effect, the acceleratio imparted to a cut varies with the number of axles actually in the retarder. The program of FIG. 2 is effective only when there are at least two trucks (at least four axles) in the retarder. Prior to that the braking effort determined by V,.,, (shown in FIG. 3) is effective. Although there will be some variation in braking effort on the cut when the number of axles in the retarder exceeds four it has been found unnecessary to take this variation into account. Balancing the increased precision obtainable against the additional complexity and time consumed by execution adequate results are obtained by ignoring variations in braking effort.

What is claimed is: 1. In a car retarder control system for a railway classification yard having a multi-position car retarder operable to different braking positions as each cut traverses said retarder for adjusting the speed at which cuts being classified couple on their assigned storage tracks, by reducing the speed of the cut from its entering velocity to a preselected exit velocity, the combination of:

means responsive to the velocity of said out when entering said retarder and to the preselected exit velocity for said out for providing a manifestation representative of each braking force to be exerted by the retarder on each cut at each instant of its travel through the retarder to reduce its velocity to said preselected exit velocity at the exit end of the retarder, means for providing a manifestation related to the position of each cut as it passes through said retarder,

and means responsive to said first recited means and said second recited means for varying the braking force exerted on each cut by said retarder as it passes through the retarder to reduce its velocity to said preselected exit velocity at the exit end of the retarder.

2. The retarder control system of claim 1 wherein the retarder is of the type which is operable to a plurality of discrete braking positions,

said first named means computing, for each cut, the

length of retarder required to reduce the speed of said out to said preselected exit velocity at the exit end of said retarder in response to the application of light braking force by said retarder, said means controlling said retarder to apply a braking force greater than light only when said computed retarder length exceeds the length of said retarder.

3. Apparatus for controlling a discrete position retarder in a railroad classification yard in order to control the coupling speed of a cut when it reaches its destination track and couples to cars preceding it, comprising,

means for determining the required length of retarder to decrease the velocity of a cut as it enters the retarder to a preselected exit velocity with light braking only,

means for comparing said previously computed length with the effective length of said retarder,

means for storing the results if the required length is less than or equal to the effective length,

and control means responsive to said means for storing to control said retarder in accordance with said stored results.

4. The apparatus of claim 3 which further comprises,

means for selecting, if said required length is greater than said actual length, a point intermediate the entrance and exit of said retarder and selecting a velocity for said cut which is intermediate the entrance and exit velocity,

means for computing the required retarder length to decrease the velocity of the cut from said selected velocity to a preselected exit velocity with light braking only,

means for comparing said last previously computed length with the length of said retarder from said intermediate point to said exit end,

and means for transmitting the results, if the required length is less than or equal to the actual length, to said means for storing.

5. The apparatus of claim 4 which further comprises,

means for incrementing the location of said intermediate point if the last computed length is greater than the length of said retarder from said intermediate point to said exit end and decrementing said selected velocity for said cut from said last selected velocity,

means for determining the required length of said retarder to decrease said selected velocity of said cut to a preselected exit velocity with light braking only,

means for comparing said previously computed length with the length of said retarder from said last selected intermediate point to the exit of said retarder,

and means for transmitting the results, is the last computed length is less than or equal to the length of said retarder from said last selected intermediate point to the exit end, to said means for storing.

6. The apparatus of claim 5 which further includes means for determining when the distance from said intermediate selected point to the entrance of said retarder is equal to or greater than the length of said retarder,

means responsive to said last named means for determining the required length of retarder to decrease the velocity of said cut as it enters the retarder to a preselected exit velocity with higher braking only,

means for comparing said previously computed length with the effective length of said retarder,

and means for transmitting the results, if the required length is less than or equal to the effective length,'

to said means for storing. 7. A method of controlling a discrete multi-position retarder in a railway classification yard comprising the steps of,

computing the necessary retarder length to decrease the velocity of a cut from its entering velocity to a preselected exit velocity, with light braking only,

comparing said necessary length with the length of said retarder,

computing and storing the time elaspsed and distance covered in reducing the velocity of said cut only if the necessary length is less than or equal to the length of the retarder, said controlling said retarder in accordance with the computed and stored time and distance. 5 8. The method of claim 7 which further comprises,

selecting, if the necessary length is greater than the length of retarder, a point intermediate. the entrance and exit of said retarder and selecting a velocity for said cut at that point which is intermediate the entrance and exit velocity, computing the required retarder length to decrease the velocity of the cut from the selected velocity to the preselected exit velocity with light braking, comparing the last previously computed length with the retarder length from said selected point to the exit end, and computing and storing the elaspsed time and distance covered in reducing the velocity only if said computed length is less than or equal to the retarder length from said selected point to the exit end. 9. The method of claim 8 which further includes the steps of, incrementing the location of said selected point as measured from the entrance end and decrementing the sleected velocity if the computed length exceeds the length of said retarder from selected point to the exit end, computing the required length of retarder to decrease said selected velocity to said preselected exit velocity with light braking only, comparing said computed length with the length of said retarder from said selected point to the exit end, computing and storing the time elapsed and distance covered in reducing the velocity to said preselected exit velocity if the computed length is less than or equal to the length of retarder from said intermediate point to the exit end. 10. The method of claim 9 which further includes the steps of,

determining where the distance from said entrance end to the incremented intermediate point is equal to or greater than the length of the retarder, computing required length of retarder to decrease the velocity of said cut as it enters the retarder to a preselected exit velocity with higher braking, comparing the previously computed length with the length of the retarder,

LII

computing and storing the elapsed time and distance to decrease the velocity to the exit velocity if said computed length is less than or equal to the length of said retarder.

11. The method of claim 8 which further includes the steps of,

defining the length of the retarder as the distance between the entrance of said retarder and said intermediate point defining said preselected exit velocity as said selected velocity, computing the retarder length necessary to decrease the entrance velocity of the exit to said preselected exit velocity at higher braking, comparing said last computed length with the length of the retarder, computing and storing the time elapsed and distance covered in reducing the velocity to the preselected exit velocity if the computed length is less than or equal to the length of the retarder. 12. Apparatus for controlling a retarder to decelerate a cut passing therethrough to a preselected exit velocity comprising,

first means for determining if light braking, only, is sufficient to decelerate said out to said preselected exit velocity and for computing the extent of said light braking if light braking, only, is sufficient, second means, responsive to said first means, for determining, if said light braking only, is insufficient, the extent, if any, of light braking to decelerate said cut to said preselected exit velocity with braking force transitions along a desired velocity-distance profile and for also determining an intermediate velocity of said out at said braking force transition,

means. 

1. In a car retarder control system for a railway classification yard having a multi-position car retarder operable to different braking positions as each cut traverses said retarder for adjusting the speed at which cuts being classified couple on their assigned storage tracks, by reducing the speed of the cut from its entering velocity to a preselected exit velocity, the combination of: means responsive to the velocity of said cut when entering said retarder and to the preselected exit velocity for said cut for providing a manifestation representative of each braking force to be exerted by the retarder on each cut at each instant of its travel through the retarder to reduce its velocity to said preselected exit velocity at the exit end of the retarder, means for providing a manifestation related to the position of each cut as it passes through said retarder, and means responsive to said first recited means and said second recited means for varying the braking force exerted on each cut by said retarder as it passes through the retarder to reduce its velocity to said preselected exit velocity at the exit end of the retarder.
 2. The retarder control system of claim 1 wherein the retarder is of the type which is operable to a plurality of discrete braking positions, said first named means computing, for each cut, the length of retarder required to reduce the speed of said cut to said preselected exit velocity at the exit end of said retarder in response to the application of light braking force by said retarder, said means controlling said retarder to apply a braking force greater than light only when said computed retarder length exceeds the length of said retarder.
 3. Apparatus for controlling a discrete position retarder in a railroad classification yard in order to control the coupling speed of a cut when it reaches its destination track and couples to cars preceding it, comprising, means for determining the required length of retarder to decreAse the velocity of a cut as it enters the retarder to a preselected exit velocity with light braking only, means for comparing said previously computed length with the effective length of said retarder, means for storing the results if the required length is less than or equal to the effective length, and control means responsive to said means for storing to control said retarder in accordance with said stored results.
 4. The apparatus of claim 3 which further comprises, means for selecting, if said required length is greater than said actual length, a point intermediate the entrance and exit of said retarder and selecting a velocity for said cut which is intermediate the entrance and exit velocity, means for computing the required retarder length to decrease the velocity of the cut from said selected velocity to a preselected exit velocity with light braking only, means for comparing said last previously computed length with the length of said retarder from said intermediate point to said exit end, and means for transmitting the results, if the required length is less than or equal to the actual length, to said means for storing.
 5. The apparatus of claim 4 which further comprises, means for incrementing the location of said intermediate point if the last computed length is greater than the length of said retarder from said intermediate point to said exit end and decrementing said selected velocity for said cut from said last selected velocity, means for determining the required length of said retarder to decrease said selected velocity of said cut to a preselected exit velocity with light braking only, means for comparing said previously computed length with the length of said retarder from said last selected intermediate point to the exit of said retarder, and means for transmitting the results, is the last computed length is less than or equal to the length of said retarder from said last selected intermediate point to the exit end, to said means for storing.
 6. The apparatus of claim 5 which further includes means for determining when the distance from said intermediate selected point to the entrance of said retarder is equal to or greater than the length of said retarder, means responsive to said last named means for determining the required length of retarder to decrease the velocity of said cut as it enters the retarder to a preselected exit velocity with higher braking only, means for comparing said previously computed length with the effective length of said retarder, and means for transmitting the results, if the required length is less than or equal to the effective length, to said means for storing.
 7. A method of controlling a discrete multi-position retarder in a railway classification yard comprising the steps of, computing the necessary retarder length to decrease the velocity of a cut from its entering velocity to a preselected exit velocity, with light braking only, comparing said necessary length with the length of said retarder, computing and storing the time elaspsed and distance covered in reducing the velocity of said cut only if the necessary length is less than or equal to the length of the retarder, said controlling said retarder in accordance with the computed and stored time and distance.
 8. The method of claim 7 which further comprises, selecting, if the necessary length is greater than the length of retarder, a point intermediate the entrance and exit of said retarder and selecting a velocity for said cut at that point which is intermediate the entrance and exit velocity, computing the required retarder length to decrease the velocity of the cut from the selected velocity to the preselected exit velocity with light braking, comparing the last previously computed length with the retarder length from said selected point to the exit end, and computing and storing the elaspsed time and distance covered in reducing the velocity only if said computed length is less than or equal to the retarder length from said selected point to the exit end.
 9. The method of claim 8 which further includes the steps of, incrementing the location of said selected point as measured from the entrance end and decrementing the sleected velocity if the computed length exceeds the length of said retarder from selected point to the exit end, computing the required length of retarder to decrease said selected velocity to said preselected exit velocity with light braking only, comparing said computed length with the length of said retarder from said selected point to the exit end, computing and storing the time elapsed and distance covered in reducing the velocity to said preselected exit velocity if the computed length is less than or equal to the length of retarder from said intermediate point to the exit end.
 10. The method of claim 9 which further includes the steps of, determining where the distance from said entrance end to the incremented intermediate point is equal to or greater than the length of the retarder, computing required length of retarder to decrease the velocity of said cut as it enters the retarder to a preselected exit velocity with higher braking, comparing the previously computed length with the length of the retarder, computing and storing the elapsed time and distance to decrease the velocity to the exit velocity if said computed length is less than or equal to the length of said retarder.
 11. The method of claim 8 which further includes the steps of, defining the length of the retarder as the distance between the entrance of said retarder and said intermediate point defining said preselected exit velocity as said selected velocity, computing the retarder length necessary to decrease the entrance velocity of the exit to said preselected exit velocity at higher braking, comparing said last computed length with the length of the retarder, computing and storing the time elapsed and distance covered in reducing the velocity to the preselected exit velocity if the computed length is less than or equal to the length of the retarder.
 12. Apparatus for controlling a retarder to decelerate a cut passing therethrough to a preselected exit velocity comprising, first means for determining if light braking, only, is sufficient to decelerate said cut to said preselected exit velocity and for computing the extent of said light braking if light braking, only, is sufficient, second means, responsive to said first means, for determining, if said light braking only, is insufficient, the extent, if any, of light braking to decelerate said cut to said preselected exit velocity with braking force transitions along a desired velocity-distance profile and for also determining an intermediate velocity of said cut at said braking force transition, third means, responsive to said second means, for determining a minimum braking level, above light braking, and the extent thereof required, to decelerate said cut to said intermediate velocity with braking force transitions along said desired velocity-distance profile, fourth means, responsive to said first, second, and third means for storing parameters associated with the respective braking levels determined by said first, second, and third means, and control means, responsive to said fourth means, to control said multi-position retarder to its various braking positions to the extent stored by said fourth means. 